The Bull At The Gate: Book 2
Book 2: 'Torc of Moonlight' trilogy. Nick has moved to York, a mediaeval city where Viking re-enactments thrill the tourists. When a colleague vanishes the police start asking awkward questions about Alice. But York was once a Roman colonia that garrisoned the Ninth Legion and the Sixth Victrix, and the stains of older, sacrificial, deaths lay buried deep in modern cellars, desperate for escape.